A typical computer system includes a power supply and one or more circuit boards (e.g., processor modules, memory modules, etc.) which are powered by the power supply. Some computer systems are equipped with both a primary power supply which converts an AC power feed from the street, and a DC battery backup power supply for fault tolerance. If the primary power supply fails and no longer provides power to computer system (e.g., if the AC power feed from the street should become unavailable), the DC battery backup power supply can take over and provide power to each circuit board of the computer system.
One conventional approach to responding to a failure of the primary power supply involves the computer system attempting to continue full operation using the DC battery backup power supply until the primary power supply becomes available again. In this approach, the DC battery backup power supply typically includes a large assembly of batteries (e.g., racks or shelves full of batteries) which, in some cases, consumes many cubic feet of space in order to store a significantly large power reserve. The computer system continues full operation using the DC battery backup power supply until the primary power supply becomes available again, or until the DC battery backup power supply runs out of power.
Another conventional approach to responding to a failure of the primary power supply involves the DC battery backup power supply providing power to the circuitry of each circuit board for a relatively short period of time (e.g., 5 to 20 minutes) to enable the computer system to perform an automated shutdown procedure which leaves the computer system in a safe and powered-down state. In this approach, the DC battery backup power supply provides power temporarily to the circuit boards of the computer system to allow each circuit board to automatically (i) complete any operations in progress, and (ii) synchronize the data in volatile memory (i.e., semiconductor memory) to a set of disk drives. At the end of the shutdown procedure, backup power to the circuit boards is turned off automatically and the computer system remains completely powered-down. When the primary power supply becomes available again, a user (e.g., a system administrator) reactivates or reboots the computer system, and the computer system can begin normal operation again.